1. Field of Invention
The invention relates to a flowmeter for measuring a liquid flow in a liquid-carrying line as well as a combination of a liquid pump for creating a liquid flow in a liquid-carrying line and a flowmeter for measuring the liquid flow.
2. Description of the Prior Art
Magnetic flowmeters, which may also be referred to as electromagnetic flowmeters or inductive flowmeters, are based on measurement of the velocity of flow of a conductive liquid through a known or controlled magnetic field by measuring the induced electric voltage. With a known flow cross section, the flow rate or volume flow can be deduced from the velocity of flow, which should be covered by the concept of liquid flow in the following discussion. An electric voltage occurs in a magnetic field through which the flow passes due to a charge separation of the ions that are present in a conductive liquid and can be measured as an induced voltage. The voltage measurement is typically performed by tapping the induced voltage on a pair of electrodes that are in electrical contact with the conductive liquid. This voltage is proportional to the velocity of flow and is independent of the magnetic field strength. The charge separation takes place in a direction perpendicular to the direction of flow and to the direction of the magnetic field. The magnetic field of a magnetic flow meter is therefore preferably arranged perpendicular to the direction of flow in the corresponding liquid channel, and the electrode pair for diverting the induced electric voltage is preferably arranged perpendicular to both the magnetic field and the direction of flow in the liquid channel.
A typical electromagnetic flowmeter is constructed from a non-magnetic and non-magnetizable tube lined on the inside with electrically insulating material.
The magnetic field is typically generated by one or more coils arranged outside of the tube through which the liquid flows. The electric voltage induced by the liquid flow is typically determined by a voltmeter, and the result of the voltage measurement is sent to an evaluation unit for determining the liquid flow, i.e., the flow rate or the volume flow based on the measured voltage.
The electric voltage tapped at the electrodes is frequently additionally influenced or disturbed by electrochemical potentials. To compensate for the influences or disturbances caused by the electrochemical potentials or to correct for them in the calculations, typically an a.c. field or an alternating field is used as the magnetic field in an electromagnetic flowmeter. The use of permanent magnets in such a configuration is therefore normally ruled out.
The object of the present invention is therefore to provide an alternative electromagnetic flowmeter.